In 3RD Generation Partnership Project Long Term Evolution (3GPP LTE), Orthogonal Frequency Division Multiplexing (OFDM) is adopted as a downlink (DL) transmission scheme.
The 3GPP LTE (Long Term Evolution) standard is the last stage in the realization of true 4th generation (4G) mobile telephone networks. Most major mobile carriers in the United States and several worldwide carriers have announced plans to convert their networks to LTE beginning in 2009. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS). Much of 3GPP Release 8 focuses on adopting 4G mobile communications technology, including an all-IP flat networking architecture.
The 3GPP LTE standard uses orthogonal frequency division multiplexing (OFDM) for the downlink (i.e., from the base station to the mobile station). Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technique that transmits on many orthogonal frequencies (or subcarriers). The orthogonal subcarriers are individually modulated and separated in frequency such that they do not interfere with one another. This provides high spectral efficiency and resistance to multipath effects.
The following documents and standards descriptions are hereby incorporated into the present disclosure as if fully set forth herein: 1) Document No. R1-101683, “Way Forward For Rel-10 Feedback Framework”, February 2010; 2) Document No. R1-102579, “Way Forward On Release 10 Feedback”, RAN WG1, April 2010; 3) Document No. RI-103419, “Way Forward on CSI Feedback Design For Rel-10 LD MIMO”, May 2010; 4) Document No. R1-103332, “Way Forward On UE Feedback”, May 2010; 5) Document No. R1-103333, “Refinements of Feedback And Codebook Design”, May 2010; 6) Document No. R1-103805, “Double Codebook Performance Evaluation”, June 2010; 7) Document No. RI-103701, “8Tx Codebook Design”, June 2010; and 8) 3GPP Technical Specification No. 36.211.
In Release 10 LTE systems, a mobile station (or user equipment) performs feedback of precoder matrix index (PMI), rank indicator (RI), and channel quality indicator (CQI) to the base station (or eNodeB). In the 3GPP RAN#60 meeting, a way forward on feedback in Release 10 was agreed upon. Release 10 uses implicit feedback of precoder matrix index (PMI), rank indicator (RI), and channel quality indicator (CQI). The user equipment (UE) or mobile station (MS) spatial feedback for a subband represents a precoder and CQI is computed based on the assumption that the eNodeB or base station (BS) uses a specific precoder (or precoders), as given by the feedback, on each subband within the CQI reference resource. It is noted that a subband may correspond to the whole system bandwidth.
A precoder for a subband is composed of two matrices. The precoder structure is applied to all transmit (Tx) antenna array configurations. Each of the two matrices belongs to a separate codebook. The codebooks are known (or synchronized) at both the base station (eNodeB) and the mobile station (user equipment). Codebooks may or may not change over time for different subbands. The two codebook indices together determine the precoder. One of the two matrices targets the wideband or long-term channel properties. The other matrix targets the frequency-selective or short-term channel properties. It is noted that a matrix codebook in this context should be interpreted as a finite, enumerated set of matrices that, for each resource block (RB), is known to both the mobile station (or UE) and the base station (or eNodeB). It is also noted that that a Release 8 precoder feedback may be deemed a special case of this structure.
Two messages are conveyed in this way: 1) Release 10 feedback will be based on implicit feedback similar to Release 8 feedback; and 2) two codebook indices will specify a precoder in Release 10, with one codebook targeting wideband and/or long-term channel properties and the other codebook targeting frequency-selective and/or short-term channel properties.
In the RAN1 #60bis meeting, another way forward on mobile station (or UE) feedback in Release 10 was also agreed upon. A precoder, W, for a subband is a function of two matrices, W1 and W2, (i.e., where W1εC1 and W2εC2). W1 is also referred to as a first PMI, and W2 is also referred to as a second PMI in this disclosure. The codebooks C1 and C2 are codebook 1 and codebook 2, respectively. The first PMI targets wideband (or long-term) channel properties. The second PMI targets frequency-selective (or short-term) channel properties. For the physical uplink control channel (PUCCH), the feedback corresponding to the first PMI and the second PMI may be sent in different or the same subframe, unless the payload is too large to send the first PMI and the second PMI in the same subframe on PUCCH. Also, periodic and aperiodic reports are independent.
Thus, there is an important difference in feedback between Release 8 (Rel-8) and Release 10 (Rel-10) of 3GPP networks. In Release 8, only one codebook index specifies a precoder. However, in Release 10, two codebook indices specify a precoder. Furthermore, these two codebook indices in Release 10 may be sent in different subframes or in the same subframe.
Therefore, there is a need in the art for improved devices and methods for providing feedback information related to CQI, PMI, and RI in Rel-10 wireless networks. In particular, there is a need in the art for improved, efficient methods and apparatuses to reduce Rel-10 feedback overhead to a level similar to Rel-8 feedback overhead.